1) I am on duty today. I was on duty that day. 
2) We are friends with Nick. We were friends with Nick. 
3) They are at school now. They were at school two days ago.
4) Ann is at home at the moment. Ann was at home yesterday.
5) She is doing her homework now. She was doing her homework that moment.
6)  My doctor is a clever moman. My doctor was is a clever moman. 
7) Her father is 37 now. Her father was 37 last year.
8) Our teacher is very young. Ouк teacher was very young. 
9) My bag is on the armchair. My bag was on the armchair.
10) Their dog is very kind. Their dog was very kind.